Scenario:
A user wants to be able to update their customer records' external ID.
Solution:
1. On your CSV Import, you must select the following Import Type and Record Type below:
2. Your CSV excel file should only contain the following columns below:
Be sure to get your company's internal ID from here:
You can instead do a Customer saved search for your customers and add "Internal ID" on the Results tab as it is different from ID, should be like this:
Once you get all the correct Internal IDs of your customers, save the csv file and attach it on your CSV Import.
3. On your Import Options, it should be "Update" only to avoid creating new records or duplicating.
4. On Field Mapping page, match your fields from your CSV to your actual NetSuite fields.
Note: The ID is mapped by default to Internal ID. Make sure that ID is not Customer ID but the system generated Internal ID.
5. Click Save and Run.